Detecting failure of a thermal sensor in a memory device

ABSTRACT

Respective values of a subset of the plurality of memory cells of a memory device are compared to a pattern of pre-programmed memory cells. The pattern pre-programmed memory cells comprise representations of values of the pattern of pre-programmed memory cells when a temperature criterion is satisfied. Responsive to determining that at least a threshold number of the respective values of the subset matches the pattern of pre-programmed memory cells, a temperature reading from a thermal sensor coupled to the memory device is identified. Responsive to determining that the temperature reading does not correspond to a temperature criterion, determining that the thermal sensor has failed.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 17/003,829, filed Aug. 26, 2020, which is incorporated byreference herein.

TECHNICAL FIELD

Embodiments of the disclosure relate generally to memory sub-systems,and more specifically, relate to detecting failure of a thermal sensorin a memory device.

BACKGROUND

A memory sub-system can include one or more memory devices that storedata. The memory devices can be, for example, non-volatile memorydevices and volatile memory devices. In general, a host system canutilize a memory sub-system to store data at the memory devices and toretrieve data from the memory devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousembodiments of the disclosure. The drawings, however, should not betaken to limit the disclosure to the specific embodiments, but are forexplanation and understanding only.

FIG. 1 illustrates an example computing system that includes a memorysub-system in accordance with some embodiments of the presentdisclosure.

FIG. 2 is a flow diagram of an example method to detect a failure of athermal sensor in a memory device, in accordance with some embodimentsof the present disclosure.

FIG. 3 illustrates a schematic diagram of a portion of non-volatilememory array in accordance with some embodiments of the presentdisclosure.

FIG. 4A depicts distributions of threshold voltages for a memory cellcapable of storing bits of data, in accordance with some embodiments ofthe present disclosure.

FIG. 4B depicts distribution of threshold voltages for a memory cellprogrammed to values in between valid states, in accordance with someembodiments of the present disclosure.

FIG. 5 is a flow diagram of an example method to detect a failure of athermal sensor in a memory device, in accordance with some embodimentsof the present disclosure.

FIG. 6 is a block diagram of an example computer system in whichembodiments of the present disclosure may operate.

DETAILED DESCRIPTION

Aspects of the present disclosure are directed to detecting a failure ofthermal sensors in a memory device within a memory sub-system. A memorysub-system can be a storage device, a memory module, or a combination ofa storage device and memory module. Examples of storage devices andmemory modules are described below in conjunction with FIG. 1 . Ingeneral, a host system can utilize a memory sub-system that includes oneor more components, such as memory devices that store data. The hostsystem can provide data to be stored at the memory sub-system and canrequest data to be retrieved from the memory sub-system.

A memory sub-system can include high density non-volatile memory deviceswhere retention of data is desired when no power is supplied to thememory device. One example of non-volatile memory devices is anegative-and (NAND) memory device. Other examples of non-volatile memorydevices are described below in conjunction with FIG. 1 . A non-volatilememory device is a package of one or more dies. Each die can consist ofone or more planes. For some types of non-volatile memory devices (e.g.,NAND devices), each plane consists of a set of physical blocks. Eachblock consists of a set of pages. Each page consists of a set of memorycells (“cells”). A cell is an electronic circuit that storesinformation. Depending on the cell type, a cell can store one or morebits of binary information, and has various logic states that correlateto the number of bits being stored. The logic states can be representedby binary values, such as “0” and “1”, or combinations of such values.

Storage of data on certain memory devices having different media typesinvolves a precise placement of electric charges into memory cells ofthe memory devices. The amount of charge placed on a memory cell can beused to represent a value stored by the memory cell. Depending on theamount of charge placed, passage of electric current through the memorycell may require an application of a value-specific threshold voltage.Readability of the memory cells depends on the distinctiveness ofthreshold voltages representing different stored values. Variations intemperature at which the memory sub-system is operated can impact thevoltages stored in and read from the memory cell.

A memory device can be connected to one or more thermal sensors that canmeasure the temperature of the memory device. A memory sub-system canuse the thermal sensor temperature reading to alert the host system ifthe memory device reaches an extreme temperature, i.e. if the memorydevice gets too hot or too cold, which can lead to failure of the memorydevice. In particular, extreme temperatures can cause the memory deviceto malfunction and/or become physically damaged. For example, the valueof a memory cell programmed to a logic state that represents a certainvalue can change when it becomes extremely hot or extremely cold. If acertain number of memory cells alter their stored values due to changesin temperature, the memory device can no longer be reliable.

Memory sub-systems can be programmed to automatically stop when athermal sensor reports extreme temperatures, and/or can send anotification to the host system to alert the host system that a memorydevice within the memory sub-system is at risk of failing. Additionallyor alternatively, the memory sub-system can report the temperaturereadings directly to the host system. Detecting and reporting memorydevice failures can be very important to functional safety. For example,undetected memory device failures in an autonomous vehicle computersystem can have catastrophic results. Hence, functioning thermal sensorscan play a critical role in helping to detect and report failures ofmemory devices within the memory sub-system.

Thermal sensors are susceptible to failure themselves. In conventionalsystems, however, a thermal sensor error or failure may go undetected.For example, a failing thermal sensor can get stuck in a loop andrepeatedly report the same temperature. If this temperature is withinthe acceptable temperature range for a memory device, the host systemand/or the memory sub-system may not detect the failure in the thermalsensor.

Aspects of the present disclosure address the above and otherdeficiencies by having a memory sub-system that can detect failure of athermal sensor in a memory device. The memory sub-system can include amemory sub-system controller that can designate a certain set of memorycells within a memory device as a specific group of cells that will beused in detecting a thermal sensor failure. The memory sub-system canprogram the designated set of memory cells to threshold voltages inbetween valid states that represent values in a specific pattern ofvalues. The memory sub-system can also store pre-programmed patterns ofcells, with one pattern representing the same specific pattern of valuesafter the cells have been exposed to extreme heat, and another patternrepresenting the same specific pattern of values after the cells havebeen exposed to extreme cold. The memory sub-system can read thedesignated set of cells within the memory device and compare the valuesof the designated set of cells to the pre-programmed patterns. If thecells match one of the patterns, the memory sub-system can determinethat the memory device is likely to be extremely hot or extremely cold,depending on which pre-programmed pattern of cells matches. The memorysub-system can then determine whether the thermal sensor has failed bydetermining whether the thermal sensor is reporting an extremely hot orextremely cold temperature.

Advantages of the present disclosure include, but are not limited to,verifying that a thermal sensor is functioning properly without theadditional expense of a redundant sensor. Such verification is criticalfor safety in many implementations, for example, autonomous driving.Some of the technical advantages include detecting memory devicefailures before the failures cause irreparable damage to the memorysub-system, thus enhancing the functioning of the memory sub-system. Thefeatures described in the present disclosure can be implemented withfirmware and do not require additional hardware. Furthermore, thefeatures described in the present disclosure avoid a single point offailure using circuitry that is independent of the regular thermalsensor scheme. Additionally, the system described in the presentdisclosure makes use of hardware that would otherwise not be used byusing non-volatile memory cells that are surplus in system blocks, thusenhancing the functioning of the memory sub-system with no addedhardware. The functioning of the memory sub-system is enhanced bydetecting and diagnosing failures that would otherwise go unnoticed,thus avoiding system failures and ensuring the proper functioning of thememory sub-system.

FIG. 1 illustrates an example computing system 100 that includes amemory sub-system 110 in accordance with some embodiments of the presentdisclosure. The memory sub-system 110 can include media, such as one ormore volatile memory devices (e.g., memory device 140), one or morenon-volatile memory devices (e.g., memory device 130), or a combinationof such.

A memory sub-system 110 can be a storage device, a memory module, or acombination of a storage device and memory module. Examples of a storagedevice include a solid-state drive (SSD), a flash drive, a universalserial bus (USB) flash drive, an embedded Multi-Media Controller (eMMC)drive, a Universal Flash Storage (UFS) drive, a secure digital (SD)card, and a hard disk drive (HDD). Examples of memory modules include adual in-line memory module (DIMM), a small outline DIMM (SO-DIMM), andvarious types of non-volatile dual in-line memory modules (NVDIMMs).

The computing system 100 can be a computing device such as a desktopcomputer, laptop computer, network server, mobile device, a vehicle(e.g., airplane, drone, train, automobile, or other conveyance),Internet of Things (IoT) enabled device, embedded computer (e.g., oneincluded in a vehicle, industrial equipment, or a networked commercialdevice), or such computing device that includes memory and a processingdevice.

The computing system 100 can include a host system 120 that is coupledto one or more memory sub-systems 110. In some embodiments, the hostsystem 120 is coupled to multiple memory sub-systems 110 of differenttypes. FIG. 1 illustrates one example of a host system 120 coupled toone memory sub-system 110. As used herein, “coupled to” or “coupledwith” generally refers to a connection between components, which can bean indirect communicative connection or direct communicative connection(e.g., without intervening components), whether wired or wireless,including connections such as electrical, optical, magnetic, etc.

The host system 120 can include a processor chipset and a software stackexecuted by the processor chipset. The processor chipset can include oneor more cores, one or more caches, a memory controller (e.g., NVDIMMcontroller), and a storage protocol controller (e.g., PCIe controller,SATA controller). The host system 120 uses the memory sub-system 110,for example, to write data to the memory sub-system 110 and read datafrom the memory sub-system 110.

The host system 120 can be coupled to the memory sub-system 110 via aphysical host interface. Examples of a physical host interface include,but are not limited to, a serial advanced technology attachment (SATA)interface, a peripheral component interconnect express (PCIe) interface,universal serial bus (USB) interface, Fibre Channel, Serial AttachedSCSI (SAS), a double data rate (DDR) memory bus, Small Computer SystemInterface (SCSI), a dual in-line memory module (DIMM) interface (e.g.,DIMM socket interface that supports Double Data Rate (DDR)), etc. Thephysical host interface can be used to transmit data between the hostsystem 120 and the memory sub-system 110. The host system 120 canfurther utilize an NVM Express (NVMe) interface to access components(e.g., memory devices 130) when the memory sub-system 110 is coupledwith the host system 120 by the physical host interface (e.g., PCIebus). The physical host interface can provide an interface for passingcontrol, address, data, and other signals between the memory sub-system110 and the host system 120. FIG. 1 illustrates a memory sub-system 110as an example. In general, the host system 120 can access multiplememory sub-systems via a same communication connection, multipleseparate communication connections, and/or a combination ofcommunication connections.

The memory devices 130, 140 can include any combination of the differenttypes of non-volatile memory devices and/or volatile memory devices. Thevolatile memory devices (e.g., memory device 140) can be, but are notlimited to, random access memory (RAM), such as dynamic random accessmemory (DRAM) and synchronous dynamic random access memory (SDRAM).

Some examples of non-volatile memory devices (e.g., memory device 130)include a negative-and (NAND) type flash memory and write-in-placememory, such as a three-dimensional cross-point (“3D cross-point”)memory device, which is a cross-point array of non-volatile memorycells. A cross-point array of non-volatile memory cells can perform bitstorage based on a change of bulk resistance, in conjunction with astackable cross-gridded data access array. Additionally, in contrast tomany flash-based memories, cross-point non-volatile memory can perform awrite in-place operation, where a non-volatile memory cell can beprogrammed without the non-volatile memory cell being previously erased.NAND type flash memory includes, for example, two-dimensional NAND (2DNAND) and three-dimensional NAND (3D NAND).

Each of the memory devices 130 can include one or more arrays of memorycells. One type of memory cell, for example, single level cells (SLC)can store one bit per cell. Other types of memory cells, such asmulti-level cells (MLCs), triple level cells (TLCs), quad-level cells(QLCs), and penta-level cells (PLCs) can store multiple bits per cell.In some embodiments, each of the memory devices 130 can include one ormore arrays of memory cells such as SLCs, MLCs, TLCs, QLCs, PLCs or anycombination of such. In some embodiments, a particular memory device caninclude an SLC portion, and an MLC portion, a TLC portion, a QLCportion, or a PLC portion of memory cells. The memory cells of thememory devices 130 can be grouped as pages that can refer to a logicalunit of the memory device used to store data. With some types of memory(e.g., NAND), pages can be grouped to form blocks.

Although non-volatile memory components such as a 3D cross-point arrayof non-volatile memory cells and NAND type flash memory (e.g., 2D NAND,3D NAND) are described, the memory device 130 can be based on any othertype of non-volatile memory, such as read-only memory (ROM), phasechange memory (PCM), self-selecting memory, other chalcogenide basedmemories, ferroelectric transistor random-access memory (FeTRAM),ferroelectric random access memory (FeRAM), magneto random access memory(MRAM), Spin Transfer Torque (STT)-MRAM, conductive bridging RAM(CBRAM), resistive random access memory (RRAM), oxide based RRAM(OxRAM), negative-or (NOR) flash memory, or electrically erasableprogrammable read-only memory (EEPROM).

A memory sub-system controller 115 (or controller 115 for simplicity)can communicate with the memory devices 130 to perform operations suchas reading data, writing data, or erasing data at the memory devices 130and other such operations. The memory sub-system controller 115 caninclude hardware such as one or more integrated circuits and/or discretecomponents, a buffer memory, or a combination thereof. The hardware caninclude a digital circuitry with dedicated (i.e., hard-coded) logic toperform the operations described herein. The memory sub-systemcontroller 115 can be a microcontroller, special purpose logic circuitry(e.g., a field programmable gate array (FPGA), an application specificintegrated circuit (ASIC), etc.), or other suitable processor.

The memory sub-system controller 115 can include a processing device,which includes one or more processors (e.g., processor 117), configuredto execute instructions stored in a local memory 119. In the illustratedexample, the local memory 119 of the memory sub-system controller 115includes an embedded memory configured to store instructions forperforming various processes, operations, logic flows, and routines thatcontrol operation of the memory sub-system 110, including handlingcommunications between the memory sub-system 110 and the host system120.

In some embodiments, the local memory 119 can include memory registersstoring memory pointers, fetched data, etc. The local memory 119 canalso include read-only memory (ROM) for storing micro-code. While theexample memory sub-system 110 in FIG. 1 has been illustrated asincluding the memory sub-system controller 115, in another embodiment ofthe present disclosure, a memory sub-system 110 does not include amemory sub-system controller 115, and can instead rely upon externalcontrol (e.g., provided by an external host, or by a processor orcontroller separate from the memory sub-system).

In general, the memory sub-system controller 115 can receive commands oroperations from the host system 120 and can convert the commands oroperations into instructions or appropriate commands to achieve thedesired access to the memory devices 130. The memory sub-systemcontroller 115 can be responsible for other operations such as wearleveling operations, garbage collection operations, error detection anderror-correcting code (ECC) operations, encryption operations, cachingoperations, and address translations between a logical address (e.g., alogical block address (LBA), namespace) and a physical address (e.g.,physical block address) that are associated with the memory devices 130.The memory sub-system controller 115 can further include host interfacecircuitry to communicate with the host system 120 via the physical hostinterface. The host interface circuitry can convert the commandsreceived from the host system into command instructions to access thememory devices 130 as well as convert responses associated with thememory devices 130 into information for the host system 120.

The memory sub-system 110 can also include additional circuitry orcomponents that are not illustrated. In some embodiments, the memorysub-system 110 can include a cache or buffer (e.g., DRAM) and addresscircuitry (e.g., a row decoder and a column decoder) that can receive anaddress from the memory sub-system controller 115 and decode the addressto access the memory devices 130.

In some embodiments, the memory devices 130 include local mediacontrollers 135 that operate in conjunction with memory sub-systemcontroller 115 to execute operations on one or more memory cells of thememory devices 130. An external controller (e.g., memory sub-systemcontroller 115) can externally manage the memory device 130 (e.g.,perform media management operations on the memory device 130). In someembodiments, memory sub-system 110 is a managed memory device, which isa raw memory device 130 having control logic (e.g., local controller132) on the die and a controller (e.g., memory sub-system controller115) for media management within the same memory device package. Anexample of a managed memory device is a managed NAND (MNAND) device.

The memory sub-system 110 includes a thermal sensor failure detectioncomponent 113 that can detect a failure of a thermal sensor connected toone or more memory devices. In some embodiments, the memory sub-systemcontroller 115 includes at least a portion of the thermal sensor failuredetection component 113. In some embodiments, the thermal sensor failuredetection component 113 is part of the host system 110, an application,or an operating system. In other embodiments, local media controller 135includes at least a portion of thermal sensor failure detectioncomponent 113 and is configured to perform the functionality describedherein.

The thermal sensor failure detection component 113 can program a subsetof cells within a memory device to voltage levels that are in between aspecific pattern of values. The thermal sensor failure detectioncomponent 113 can also identify pre-programmed patterns within thememory device. The patterns can represent the same specific pattern ofvalues that was programmed to the subset of memory cells, except thatthe pre-programmed patterns are stored within the memory device afterhaving been exposed to extreme temperatures. For example, upon assembly,the memory cells on which a first pre-programmed pattern is stored canbe placed under extreme heat for a certain amount of time. When memorycells are exposed to extreme temperatures, the values stored on thememory cells can change. Hence, after having been exposed to extremeheat, the first pre-programmed pattern can represent the values that thespecific pattern of values changes to under extreme heat. The memorycells on which a second pre-programmed pattern is stored can be placedunder extreme cold for a certain amount of time. The secondpre-programmed pattern can represent the values that the specificpattern changes to under extreme cold. Extreme heat can be defined asabove 85 degrees Celsius, and extreme cold can be defined as below minus10 degrees Celsius, for example, although the extreme temperatures arenot limited to these ranges. Nominal temperature for a memory device canbe between minus 10 and 85 degrees Celsius, for example. In oneembodiment, the memory cells in the patterns are not actually exposed tothe extreme hot and cold temperatures, but rather are programmed torepresent what the values would look like if the memory cells had beenexposed to the extreme temperatures.

The subset of cells programmed to voltage levels in between validstates, and/or the memory cells stored as pre-programmed patterns ofcells after having been exposed to extreme temperatures, can be storedin memory cells within memory device 130 that are otherwise unused. Forexample, memory devices, such as memory device 130, can include a largearray of memory cells that are reserved as system blocks but that oftenend up not being used. The pre-programmed patterns of cells, as well asthe subset of cells programmed to threshold values in-between validstates, can be cells that are within the unused array of memory cellswithin memory device 130.

Additionally, the subset of cells programmed to voltage levels inbetween valid states can be in multiple memory devices within memorysub-system 110. For example, memory sub-system 110 can include multiplenon-volatile memory devices (such as memory device 130). The multiplememory devices can have one thermal sensor 133 connected to them, and insome instances, the closer the memory device is to the thermal sensor133, the more reliable the reading can be. So while the reading fromthermal sensor 133 can be accurate for the memory device(s) located nearthe thermal sensor 133, the reading from thermal sensor 133 can be lessaccurate for the memory device(s) located further away from the thermalsensor 133. Thermal sensor failure detection component 113 can programthe subset of cells to voltage levels in between valid states in memorycells spread throughout all the memory devices 130 within memorysub-system 110, including both memory devices close to the thermalsensor 133 and memory devices not close to the thermal sensor 133.Alternatively, thermal sensor failure detection component 113 canprogram the subset of cells to voltage levels between valid states inmemory devices far away from the thermal sensor 133.

The thermal sensor failure detection component 113 can then read thesubset of cells that were originally programmed to voltage levelsbetween the valid states in the specific pattern of values, and comparethe subset of cells to the pre-programmed patterns. Upon determiningthat the subset of cells match one of the pre-programmed patterns, thethermal sensor failure detection component 113 can determine that thememory device is either extremely hot or extremely cold, depending onwhich pattern matches. The thermal sensor failure detection component113 can compare a reading from a thermal sensor 133 connected to the oneor more memory devices to determine whether the thermal sensor 133 hasfailed. For example, the thermal sensor failure detection component 113can determine that the thermal sensor 133 has failed if the subset ofcells matches the extremely hot pre-programmed pattern, but thermalsensor 133 reads a nominal temperature.

Upon determining that the thermal sensor 133 has failed, the thermalsensor failure detection component 113 can send a notification to thehost system 120. The thermal sensor failure detection component 113 canperform the failure detection operations as background operations atpreset intervals, for example, every 5 minutes, and send a notification,or an interrupt, to the host system 120 upon detecting a thermal sensorfailure. Additionally or alternatively, the host system 120 can requestthat the memory sub-system 110 perform the failure detection operationsdescribed herein. Additionally or alternatively, the memory sub-system110, through controller 115 and/or the local controller 135, candetermine that the temperature readings from a thermal sensor 133 areirregular, and can then execute the failure detection operationsdescribed herein to determine whether the thermal sensor 133 isfunctioning properly. For example, the memory sub-system controller 115and/or the local controller 135 can detect that the thermal sensor 133may be malfunctioning if it repeatedly reports the same temperature fora specific amount of time. Upon detecting a potential malfunction, thememory sub-system controller 115 and/or the local controller 135 canperform the operations described herein to confirm whether the thermalsensor 133 is functioning properly. Further details with regards to theoperations of the thermal sensor failure detection component 113 aredescribed below.

In certain embodiments, the memory sub-system 110 and/or the host system120, upon determining that a thermal sensor has filed, can switch overto a different set of memory devices in order to maintain safefunctionality of the computer system.

FIG. 2 is a flow diagram of an example method 200 to detect a failure ofa thermal sensor in a memory device, in accordance with some embodimentsof the present disclosure. The method 200 can be performed by processinglogic that can include hardware (e.g., processing device, circuitry,dedicated logic, programmable logic, microcode, hardware of a device,integrated circuit, etc.), software (e.g., instructions run or executedon a processing device), or a combination thereof. In some embodiments,the method 200 is performed by the thermal sensor failure detectioncomponent 113 of FIG. 1 . Although shown in a particular sequence ororder, unless otherwise specified, the order of the processes can bemodified. Thus, the illustrated embodiments should be understood only asexamples, and the illustrated processes can be performed in a differentorder, and some processes can be performed in parallel. Additionally,one or more processes can be omitted in various embodiments. Thus, notall processes are required in every embodiment. Other process flows arepossible.

At operation 210, the processing logic can perform a program operationon a subset of a plurality of memory cells. The program operation caninclude programming the subset of memory cells to voltages between validstates. The valid states can represent a specific pattern of values.Programming memory cells to voltages between valid states is furtherdescribed with respect to FIGS. 4A and 4B.

At operation 220, the processing logic can perform a sense operation(e.g., a read operation) on the subset of the plurality of memory cellsto determine respective values stored in the subset of the plurality ofmemory cells. Because the subset was programmed at voltages betweenvalid states, the memory cells have a higher likelihood of experiencinga change in value when the temperature of the memory device has reachedextreme levels.

At operation 230, the processing logic can identify one or more patternsof pre-programmed cells. The pre-programmed patterns can include a firstpattern that represents values of the pre-programmed memory cellssatisfying a first temperature criterion, and a second pattern thatrepresents values of the pre-programmed cells satisfying a secondtemperature criterion. The values of the pre-programmed memory cells inthe first pattern can represent memory cells that have been programmedto the specific pattern of values and then exposed to a temperature thatsatisfies a first temperature criterion, i.e., a temperature thatexceeds a first temperature threshold (e.g., 85 degrees Celsius). Thevalues of the pre-programmed memory cells in the second pattern canrepresent memory cells that have been programmed to the specific patternof values and then exposed to a temperature that satisfies a secondtemperature criterion, i.e., a temperature that is below a secondtemperature threshold (e.g., minus 10 degrees Celsius). The values ofthe pre-programmed memory cells in the first and second patterns arefurther described with respect to FIG. 3 .

At operation 240, the processing logic can compare the respective valuesof the subset of the plurality of memory cells to the values of thepre-programmed memory cells in the one or more patterns. The processinglogic can determine that the values of the subset of memory cellsmatches one of the patterns by determining that a certain number ofcells within the subset match the cells in the pattern, or bydetermining that a certain percentage of the cells within the subsetmatch the cells in the pattern. That is, when comparing the subset ofcells to the one or more patterns, the processing logic can determine amatch even if not every single memory cell value in the sets match. Theprocessing logic can determine that the sets of cells substantiallymatch based on a threshold number of cells matching, or a thresholdpercentage, for example.

At operation 250, the processing logic can determine, based on thecomparison, whether a reading from a thermal sensor coupled to thememory device satisfies an accuracy criterion. In response todetermining that the reading from the thermal sensor does not satisfythe accuracy criterion, the processing logic can send a notification tothe host system.

In determining whether the reading from the thermal sensor satisfies theaccuracy criterion, the processing logic can determine whether thereading is above a temperature threshold value or below a temperaturethreshold value, depending on which pattern of pre-programmed cells thesubset of cells matches. That is, if the subset of memory cells matches(or substantially matches) the first pattern of pre-programmed cells,the processing logic can determine that the memory device is runninghot. The processing logic can determine whether the thermal sensor isfailing by comparing the reading to the “hot” temperature threshold. Forexample, a memory device can be considered to be running hot when afunctioning thermal sensor connected to the memory device reads above 85degrees Celsius. The processing logic can determine that thermal sensoris failing if the subset of memory cells matches the first pattern butthe reading from the thermal sensor does not exceed 85 degrees Celsius.

A similar analysis can be done using a “cold” temperature threshold.That is, if the subset of memory cells matches (or substantiallymatches) the second pattern of pre-programmed cells, the processinglogic can determine that the memory device is running cold. Theprocessing logic can determine whether the thermal sensor is failing bycomparing the reading to the “cold” temperature threshold. For example,a memory device can be considered to be running cold when a functioningthermal sensor connected to the memory device reads below minus 10degrees Celsius. The processing logic can determine that thermal sensoris failing if the subset of memory cells matches the second pattern butthe reading from the thermal sensor is not below minus 10 degreesCelsius.

FIG. 3 illustrates a schematic diagram of a portion of a non-volatilememory array in accordance with a number of embodiments of the presentdisclosure. The memory array can be contained within one or more memorydevices, such as memory device 130 illustrated in FIG. 1 . Theembodiment of FIG. 3 illustrates a NAND architecture non-volatile memoryarray. However, embodiments described herein are not limited to thisexample. A memory device can be made up of bits arranged in atwo-dimensional grid. The memory array 301 includes memory cells 311-1to 311-N, 312-1 to 312-N, 313-1 to 313-N that are etched onto a siliconwafer in an array of columns 307-1 to 307-M (also hereinafter referredto as bitlines) and rows 305-1 to 305-N (also hereinafter referred to aswordlines). A wordline can refer to one or more rows of memory cells ofa memory device that are used with one or more bitlines to generate theaddress of each of the memory cells. The intersection of a bitline andwordline constitutes the address of the memory cell. A block hereinafterrefers to a unit of the memory device used to store data and can includea group of memory cells, a wordline group, a wordline, or individualmemory cells. One or more blocks can be grouped together to form a planeof the memory device in order to allow concurrent operations to takeplace on each plane. The memory device can include circuitry thatperforms concurrent memory page accesses of two or more memory planes.For example, the memory device can include a respective access linedriver circuit and power circuit for each plane of the memory device tofacilitate concurrent access of pages of two or more memory planes,including different page types.

As shown in FIG. 3 , the memory array 301 includes a number of NANDstrings, where each NAND string includes non-volatile memory cells 311-1to 311-N, each communicatively coupled to a respective wordline 305-1 to305-N. Each NAND string (and its constituent memory cells) is alsoassociated with a local bitline (i.e., one of local bitlines 307-1 to307-M). The memory cells 311-1 to 311-N of each NAND string are coupledin series, source to drain, between a source select gate (SGS) and adrain select gate (SGD). Each source select gate is configured toselectively couple a respective NAND string to a common sourceresponsive to a signal on source the select line, while each drainselect gate is configured to selectively couple a respective NAND stringto a respective bitline responsive to a signal on the drain select line.

In a number of embodiments, construction of the non-volatile memorycells 311-1 to 311-N includes a source, a drain, a floating gate orother charge storage structure, and a control gate. The memory cells311-1 to 311-N have their control gates coupled to a wordline, 305-1 to305-N, respectively. A number (e.g., a subset or all) of cells coupledto a selected wordline can be written and/or read together as a group. Anumber of cells written and/or read together can correspond to a page ofdata. As used herein, examples of high-level operations are referred toas writing or reading operations (e.g., from the perspective of acontroller), whereas, with respect to the memory cells, such operationsare referred to as programming or sensing. A group of cells coupled to aparticular wordline and programmed together to respective states can bereferred to as a target page. A programming operation can includeapplying a number of program pulses (e.g., 16V-20V) to a selected wordline in order to increase the threshold voltage (Vt) of selected cellscoupled to that selected word line to a desired program voltage levelcorresponding to a targeted state. Read operations can include sensing avoltage and/or current change of a bitline coupled to a selected cell inorder to determine the state of the selected cell. The read operationcan include precharging a bitline and sensing the discharge when aselected cell begins to conduct.

According to some embodiments of the present disclosure, memorysub-system 110 can store (on local memory 119, for example) the valuesof a pre-programmed pattern of memory cells that have been exposed toextreme heat and to extreme cold. For example, memory cells 311-1 to311-N can have been programmed to a specific pattern of values and thenexposed to extreme heat for a certain amount of time. The values ofmemory cells 311-1 to 311-N after having been exposed to extreme heat(referred to the first pattern of pre-programmed cells) can then bestored in memory sub-system 110 (e.g., on local memory 119). To furtherthe example, memory cells 312-1 to 312-N can have been programmed to thesame specific pattern of values and then exposed to extreme cold for acertain amount of time. The values of memory cells 312-1 to 312-N afterhaving been exposed to extreme cold (referred to the second pattern ofpre-programmed cells) can then be stored in memory sub-system 110 (e.g.,on local memory 119). In some embodiments, the memory cells programmedto voltage levels in between valid states, as well as the memory cellsused to store the pre-programmed patterns representing the valid statesafter having been exposed to extreme temperatures, can be stored in morethan one managed NAND device, and need not be consecutive as is depictedin FIG. 3 .

Thermal sensor failure detection component 113 of FIG. 1 can program asubset of cells (e.g., 313-1 to 313-N) to voltage levels correspondingto a targeted state that represents in-between valid states. The validstates can be the same as the specific pattern of values that memorycells 311-1 to 311-N and 312-1 to 312-N were programmed to before beingexposed to extreme temperatures. Memory cells 313-1 to 313-N, however,can be programmed to voltage levels that represent values in between thespecific pattern of values. For example, if the programming operation toprogram memory cells 311-1 to 311-N included applying a number ofprogram pulses between 16V and 20V, then the programming operation toprogram memory cells 313-1 to 313-N can include applying a number ofprogram pulses between 18V and 22V.

Thermal sensor failure detection component 113 can then read the subsetof cells (memory cells 313-1 to 313-N in this example) and compare thevalues to the first and second patterns of pre-programmed cells (in thisexample, memory cells 311-1 to 311-N and 312-1 to 312-N respectively).Based on this comparison, thermal sensor failure detection component 113can determine whether the memory sub-system is running extremely hot,extremely cold, or at a nominal temperature. Specifically, if the memorycells 313-1 to 313-N match the first pattern of pre-programmed cells,thermal sensor failure detection component 113 can determine that thememory sub-system is running extremely hot, since the memory cells 313-1to 313-N match the cells that have previously been exposed to extremeheat. Similarly, if the memory cells 313-1 to 313-N match the secondpattern of pre-programmed cells, thermal sensor failure detectioncomponent 113 can determine that the memory sub-system is runningextremely cold, since the memory cells 313-1 to 313-N match the cellsthat have previously been exposed to extreme cold.

The subset of cells programmed to values in between valid states doesnot need to match every cell in the first pattern or the second patternin order for the sensor failure detection component 113 to determinethat the cells match the pattern. For example, the memory sub-system 110and/or the host system 120 can set a threshold number of cells that needto match in order to be considered a match, or a threshold percentage ofcells that need to match. For example, the threshold percentage can beset to 80%, and so if the thermal sensor failure detection component 113determines that 80% or more of the cells in the subset of cells (e.g.,memory cells 313-1 to 313-N) match the values in the first pattern ofpre-programmed cells, then the thermal sensor failure detectioncomponent 113 can determine that the memory device is running extremelyhot.

Thermal sensor failure detection component 113 can then determinewhether the thermal sensor has failed by determining whether a readingfrom the thermal sensor attached to the memory device reads as extremelyhot (e.g., above 85 degrees Celsius) or extremely cold (e.g., belowminus 10 degrees Celsius), as the case may be. For example, if thesubset of cells (e.g., memory cells 313-a to 313-N) match (orsubstantially match) the first pattern of pre-programmed cells, and thereading from the thermal sensor reads below 85 degrees Celsius, thethermal sensor failure detection component 113 can determine that thethermal sensor has failed. Similarly, if the subset of cells (e.g.,memory cells 313-a to 313-N) match (or substantially match) the secondpattern of pre-programmed cells, and the reading from the thermal sensorreads above minus 10 degrees Celsius, the thermal sensor failuredetection component 113 can determine that the thermal sensor hasfailed.

In some embodiments, in response to determining that the subset of cells(e.g., memory cells 313-a to 313-N) do not match (or substantiallymatch) the first or the second pattern of pre-programmed cells, thethermal sensor failure detection component 113 can determine that thethermal sensor has failed if the reading from the thermal sensor is notnominal, i.e., is the extremely high threshold or below the extremelylow threshold.

FIGS. 4A and 4B illustrate various possible threshold voltagedistributions for programmed states in accordance with a number ofembodiments of the present disclosure. The examples shown in FIGS. 4Aand 4B can represent, for example, memory cells in a block of memorydevice 130, previously described in connection with FIG. 1 . In someembodiments, the distributions shown in FIGS. 4A and 4B can describestates of transistor-based memory cells, such asmetal-oxide-semiconductor field effect transistor (MOSFET) memory cells.

FIG. 4A depicts distributions of threshold voltages for a memory cellcapable of storing for bits of data, in accordance with some embodimentsof the present disclosure. The example shown in FIG. 4A represents 16different charge states of a memory cell configured as quad-level cell(QLC) memory. The numbers 0, 1, . . . 15 enumerate various states of thememory cell. For example, a memory cell programmed into a charge state 0can represent stored value 1111, state 1 can represent stored value0111, state 2 can represent stored value 0011, and so on. However,embodiments of the present disclosure are not limited to this example.

The memory sub-system can have a certain set of memory cells that havebeen programmed to threshold voltages representing valid states, asillustrated in FIG. 4A. A first set of cells programmed to a certainpattern of valid states can be exposed to extreme heat, above atemperature threshold (e.g., above 85 degrees Celsius), and a second setof cells programmed to the same pattern of valid states can be exposedto extreme cold, below a temperature threshold (e.g., below minus 10degrees Celsius). The values of these sets of cells can then be saved,for example on local memory 119. It can be expected that the value of acertain number of memory cells will have changed as a result of havingbeen exposed to extreme temperatures.

FIG. 4B illustrates a diagram 450 of threshold voltage distributions forprogrammed values in between valid states, in accordance with a numberof embodiments of the present disclosure. Depicted in FIG. 4B aredistributions 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, . . . , 14.5 which representdistributions of voltages between valid states in a memory cellconfigured as QLC memory. That is, the voltage levels are shifted to thevalleys in between the valid states.

When there is not enough separation between respective threshold voltageof two consecutive states (or bit levels), an error can occur, such as abit flip. Typically, as described above, each binary value stored in amemory cell has a different threshold voltage associated with it, withthe lowest binary value having the highest threshold voltage, thehighest binary value having the lowest threshold voltage, andintermediate states having progressively different threshold voltagevalues. For example, a memory cell configured as QLC memory has sixteenstates, each state having a corresponding V_(t), as depicted in FIG. 4A.

FIG. 4B depicts the threshold voltages of the subset of cells that thethermal sensor failure detection component 113 can use in determiningwhether the thermal sensor has failed. As the level separation involtages become shifted due to changes in environmental conditions, thevalues stored in the memory cells can change (or flip). The subset ofcells that are programmed to levels between valid states, as depicted inFIG. 4B, have a higher likelihood of shifting when exposed to extremetemperatures, since the cells are already partly shifted. That is, byplacing the voltage level between valid states, the cell is likely toread as one value at one temperature range, and another value at anothertemperature range. As such, the thermal sensor failure detectioncomponent 113 is more likely to determine that the memory device isrunning at an extreme temperature when reading the voltage levels of thecells that have been programmed to in-between valid states.

FIG. 5 is a flow diagram of an example method 500 to detect a failure ofa thermal sensor in a memory device, in accordance with some embodimentsof the present disclosure. The method 500 can be performed by processinglogic that can include hardware (e.g., processing device, circuitry,dedicated logic, programmable logic, microcode, hardware of a device,integrated circuit, etc.), software (e.g., instructions run or executedon a processing device), or a combination thereof. In some embodiments,the method 500 is performed by the thermal sensor failure detectioncomponent 113 of FIG. 1 . Although shown in a particular sequence ororder, unless otherwise specified, the order of the processes can bemodified. Thus, the illustrated embodiments should be understood only asexamples, and the illustrated processes can be performed in a differentorder, and some processes can be performed in parallel. Additionally,one or more processes can be omitted in various embodiments. Thus, notall processes are required in every embodiment. Other process flows arepossible.

At operation 510, the processing logic can read data from a subset of aplurality of memory cells within the memory device. The plurality ofmemory cells within the memory device can include a first pattern ofpre-programmed memory cells representing values corresponding to a firsttemperature range, and a second pattern of pre-programmed cellsrepresenting values corresponding to a second temperature range. Thatis, the pre-programmed patterns of memory cells within the plurality ofmemory cells each represent values of a memory cells that wereprogrammed to a specific pattern of values, and then exposed to atemperature range. For example, the first pattern of pre-programmedcells can represent the values of the memory cells programmed to thespecific pattern after it has been exposed to extreme heat (e.g., afirst temperature range that includes temperatures above 85 degreesCelsius) for a certain period of time. The second pattern ofpre-programmed cells can represent the values of the memory cellsprogrammed to the same specific pattern after being exposed to extremecold (e.g., a second temperature range that includes temperatures belowminus 10 degrees Celsius) for a certain period of time. Exposing thememory cells to extreme temperatures can alter their states (i.e., alterthe values stored within the memory cells), and can represent the valuesthat the specific pattern change to when exposed to extremetemperatures. In one embodiment, the memory cells in the patterns arenot actually exposed to the extreme hot and cold temperatures, butrather are programmed to represent what the values would look like ifthe memory cells had been exposed to the extreme temperatures.

The subset of plurality of memory cells that the processing logic canread at operation 510 can be separate from the first and second patternsof pre-programmed cells. In some embodiments, prior to reading the datafrom the subset of memory cells, the processing logic can havepreviously programmed the subset of cells to voltage levels betweenvalid states. The valid states can represent a specific pattern ofvalues. Programming memory cells to voltages between valid states isfurther described with respect to FIGS. 4A and 4B.

At operation 520, the processing logic can compare the data from thesubset of the plurality of memory cells to the first pattern and/or thesecond pattern of pre-programmed memory cells. Comparing the subset ofcells to the first and/or second patterns can include determining that athreshold number of the values in the subset match the values in thefirst pattern and/or second pattern. That is, not every cell in thesubset needs to match the first pattern or second pattern in order todetermine that the subset matches the first pattern or second pattern.The processing logic can determine that the sets of cells substantiallymatch based on a threshold number of cells matching, or a thresholdpercentage, for example.

At operation 530, in response to determining that the data from thesubset of cells matches either the first pattern or the second pattern,the processing logic can determine whether the memory device is runningat a temperature that falls within the temperature range correspondingto the matched pattern of pre-programmed cells. The memory device caninclude a thermal sensor configured to monitor the operating temperaturein the memory sub-system. The processing logic can determine whether thethermal sensor indicates a temperature reading corresponding to eitherthe first temperature or the second temperature range.

At operation 540, in response to determining that the temperaturereading of the thermal sensor does not correspond to either the first orthe second temperature range, the processing logic can generate anotification indicating a failure of the thermal sensor. The processinglogic can transmit the notification to a host system.

In on embodiment, in response to determining that the data from thesubset of cells does not match either the first pattern or the secondpattern of pre-programmed cells, the processing logic can check whetherthe thermal sensor is functioning properly by determining whether thethermal sensor indicates a nominal temperature. Hence, when the subsetof cells does not match either the first pattern or the second pattern,the processing logic can determine whether the temperature reading ofthe thermal sensor corresponds to one of the temperature ranges.Responsive to determining that the temperature reading corresponds toone either the first or second temperature range (i.e., the temperaturereading falls within one of the extreme temperature ranges and is notnominal), the processing logic can generate a notification indicating afailure of the thermal sensor. The processing logic can transmit thenotification to a host system.

FIG. 6 illustrates an example machine of a computer system 600 withinwhich a set of instructions, for causing the machine to perform any oneor more of the methodologies discussed herein, can be executed. In someembodiments, the computer system 600 can correspond to a host system(e.g., the host system 120 of FIG. 1 ) that includes, is coupled to, orutilizes a memory sub-system (e.g., the memory sub-system 110 of FIG. 1) or can be used to perform the operations of a controller (e.g., toexecute an operating system to perform operations corresponding to thethermal sensor failure detection component 113 of FIG. 1 ). Inalternative embodiments, the machine can be connected (e.g., networked)to other machines in a LAN, an intranet, an extranet, and/or theInternet. The machine can operate in the capacity of a server or aclient machine in client-server network environment, as a peer machinein a peer-to-peer (or distributed) network environment, or as a serveror a client machine in a cloud computing infrastructure or environment.

The machine can be a personal computer (PC), a tablet PC, a set-top box(STB), a Personal Digital Assistant (PDA), a cellular telephone, a webappliance, a server, a network router, a switch or bridge, or anymachine capable of executing a set of instructions (sequential orotherwise) that specify actions to be taken by that machine. Further,while a single machine is illustrated, the term “machine” shall also betaken to include any collection of machines that individually or jointlyexecute a set (or multiple sets) of instructions to perform any one ormore of the methodologies discussed herein.

The example computer system 600 includes a processing device 602, a mainmemory 604 (e.g., read-only memory (ROM), flash memory, dynamic randomaccess memory (DRAM) such as synchronous DRAM (SDRAM) or RDRAM, etc.), astatic memory 606 (e.g., flash memory, static random access memory(SRAM), etc.), and a data storage system 618, which communicate witheach other via a bus 630.

Processing device 602 represents one or more general-purpose processingdevices such as a microprocessor, a central processing unit, or thelike. More particularly, the processing device can be a complexinstruction set computing (CISC) microprocessor, reduced instruction setcomputing (RISC) microprocessor, very long instruction word (VLIW)microprocessor, or a processor implementing other instruction sets, orprocessors implementing a combination of instruction sets. Processingdevice 602 can also be one or more special-purpose processing devicessuch as an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA), a digital signal processor (DSP),network processor, or the like. The processing device 602 is configuredto execute instructions 626 for performing the operations and stepsdiscussed herein. The computer system 600 can further include a networkinterface device 608 to communicate over the network 620.

The data storage system 618 can include a machine-readable storagemedium 624 (also known as a computer-readable medium) on which is storedone or more sets of instructions 626 or software embodying any one ormore of the methodologies or functions described herein. Theinstructions 626 can also reside, completely or at least partially,within the main memory 604 and/or within the processing device 602during execution thereof by the computer system 600, the main memory 604and the processing device 602 also constituting machine-readable storagemedia. The machine-readable storage medium 624, data storage system 618,and/or main memory 604 can correspond to the memory sub-system 110 ofFIG. 1 .

In one embodiment, the instructions 626 include instructions toimplement functionality corresponding to a thermal sensor failuredetection component (e.g., the thermal sensor failure detectioncomponent 113 of FIG. 1 ). While the machine-readable storage medium 624is shown in an example embodiment to be a single medium, the term“machine-readable storage medium” should be taken to include a singlemedium or multiple media that store the one or more sets ofinstructions. The term “machine-readable storage medium” shall also betaken to include any medium that is capable of storing or encoding a setof instructions for execution by the machine and that cause the machineto perform any one or more of the methodologies of the presentdisclosure. The term “machine-readable storage medium” shall accordinglybe taken to include, but not be limited to, solid-state memories,optical media, and magnetic media.

Some portions of the preceding detailed descriptions have been presentedin terms of algorithms and symbolic representations of operations ondata bits within a computer memory. These algorithmic descriptions andrepresentations are the ways used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of operations leading to adesired result. The operations are those requiring physicalmanipulations of physical quantities. Usually, though not necessarily,these quantities take the form of electrical or magnetic signals capableof being stored, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. The presentdisclosure can refer to the action and processes of a computer system,or similar electronic computing device, that manipulates and transformsdata represented as physical (electronic) quantities within the computersystem's registers and memories into other data similarly represented asphysical quantities within the computer system memories or registers orother such information storage systems.

The present disclosure also relates to an apparatus for performing theoperations herein. This apparatus can be specially constructed for theintended purposes, or it can include a general purpose computerselectively activated or reconfigured by a computer program stored inthe computer. Such a computer program can be stored in a computerreadable storage medium, such as, but not limited to, any type of diskincluding floppy disks, optical disks, CD-ROMs, and magnetic-opticaldisks, read-only memories (ROMs), random access memories (RAMs), EPROMs,EEPROMs, magnetic or optical cards, or any type of media suitable forstoring electronic instructions, each coupled to a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general purposesystems can be used with programs in accordance with the teachingsherein, or it can prove convenient to construct a more specializedapparatus to perform the method. The structure for a variety of thesesystems will appear as set forth in the description below. In addition,the present disclosure is not described with reference to any particularprogramming language. It will be appreciated that a variety ofprogramming languages can be used to implement the teachings of thedisclosure as described herein.

The present disclosure can be provided as a computer program product, orsoftware, that can include a machine-readable medium having storedthereon instructions, which can be used to program a computer system (orother electronic devices) to perform a process according to the presentdisclosure. A machine-readable medium includes any mechanism for storinginformation in a form readable by a machine (e.g., a computer). In someembodiments, a machine-readable (e.g., computer-readable) mediumincludes a machine (e.g., a computer) readable storage medium such as aread only memory (“ROM”), random access memory (“RAM”), magnetic diskstorage media, optical storage media, flash memory components, etc.

In the foregoing specification, embodiments of the disclosure have beendescribed with reference to specific example embodiments thereof. Itwill be evident that various modifications can be made thereto withoutdeparting from the broader spirit and scope of embodiments of thedisclosure as set forth in the following claims. The specification anddrawings are, accordingly, to be regarded in an illustrative senserather than a restrictive sense.

What is claimed is:
 1. A system comprising: a memory device comprising aplurality of memory cells; and a processing device, operatively coupledwith the memory device, to perform operations comprising: comparingrespective values of a subset of the plurality of memory cells to apattern of pre-programmed memory cells on the memory device, wherein thepattern of pre-programmed memory cells comprises representations ofvalues of the pattern of pre-programmed memory cells when a temperaturecriterion is satisfied; responsive to determining that at least athreshold number of the respective values of the subset matches thepattern of pre-programmed memory cells, identifying a temperaturereading from a thermal sensor coupled to the memory device; andresponsive to determining that the temperature reading does notcorrespond to the temperature criterion, determining that the thermalsensor has failed.
 2. The system of claim 1, wherein the processingdevice is to perform operations further comprising: programming thesubset of the plurality of memory cells to voltages between valid statesof the memory cells.
 3. The system of claim 1, wherein the processingdevice is to perform operations further comprising: responsive todetermining that the thermal sensor has failed, sending a notificationto a host system.
 4. The system of claim 1, wherein the processingdevice is to perform operations further comprising: performing a programoperation on the subset of the plurality of memory cells; and performinga sense operation on the subset of the plurality of memory cells todetermine the respective values stored in the subset of the plurality ofmemory cells.
 5. The system of claim 1, wherein the temperaturecriterion is satisfied in response to determining that the patternrepresents at least one of: a first set of cells programmed at a firsttemperature exceeding a first temperature threshold, or a second set ofcells programmed at a second temperature below a second temperaturethreshold.
 6. The system of claim 1, wherein the processing device is toperform operations further comprising: responsive to determining that anumber of temperature readings over a certain time period satisfies acriterion, performing the comparing of the respective values of thesubset of the plurality of memory cells to the pattern of pre-programmedmemory cells on the memory device.
 7. The system of claim 6, wherein thecriterion is satisfied by determining that respective values of thenumber of temperature readings over the certain time period match. 8.The system of claim 1, wherein the processing device performs theoperations at a predetermined time interval.
 9. A method comprising:comparing respective values of a subset of a plurality of memory cellsof a memory device to a pattern of pre-programmed memory cells of thememory device, wherein the pattern of pre-programmed memory cellscomprises representations of values of the pattern of pre-programmedmemory cells when a temperature criterion is satisfies; responsive todetermining that at least a threshold number of the respective values ofthe subset matches the pattern of pre-programmed memory cells,identifying a temperature reading from a thermal sensor coupled to thememory device; and responsive to determining that the temperaturereading does not correspond to the temperature criterion, determiningthat the thermal sensor has failed.
 10. The method of claim 9, furthercomprising: programming the subset of the plurality of memory cells tovoltages between valid states of the memory cells.
 11. The method ofclaim 9, further comprising: responsive to determining that the thermalsensor has failed, sending a notification to a host system.
 12. Themethod of claim 9, further comprising: performing a program operation onthe subset of the plurality of memory cells; and performing a senseoperation on the subset of the plurality of memory cells to determinethe respective values stored in the subset of the plurality of memorycells.
 13. The method of claim 9, wherein the temperature criterion issatisfied in response to determining that the pattern represents atleast one of: a first set of cells programmed at a first temperatureexceeding a first temperature threshold, or a second set of cellsprogrammed at a second temperature below a second temperature threshold.14. The method of claim 9, further comprising: responsive to determiningthat a number of temperature readings over a certain time periodsatisfies a criterion, performing the comparing of the respective valuesof the subset of the plurality of memory cells to the pattern ofpre-programmed memory cells on the memory device.
 15. The method ofclaim 14, wherein the criterion is satisfied by determining thatrespective values of the number of temperature readings over the certaintime period match.
 16. The method of claim 9, wherein the comparison isperformed at a predetermined time interval.
 17. A memory sub-systemcomprising: a memory device comprising a plurality of memory cells, theplurality of memory cells including a pattern of pre-programmed memorycells representing values corresponding to a temperature range; athermal sensor configured to monitor an operating temperature in thememory sub-system; and a processing device, operatively coupled with thememory device, to perform operations comprising: comparing respectivevalues of a subset of the plurality of memory cells the pattern ofpre-programmed memory cells; responsive to determining that at least athreshold number of the respective values of the subset matches thepattern of pre-programmed memory cells, identifying a temperaturereading from the thermal sensor; and responsive to determining that thetemperature reading does not correspond to the temperature range,determine that the thermal sensor has failed.
 18. The memory sub-systemof claim 17, wherein the processing device is to perform operationsfurther comprising: programming the subset of the plurality of memorycells to voltages between valid states of the memory cells; and readingdata from the subset of the plurality of memory cells.
 19. The memorysub-system of claim 17, wherein the temperature range represents atleast one of: temperatures above a first temperature threshold value ortemperatures below a second temperature threshold value.
 20. The memorysub-system of claim 17, wherein the processing device is to performoperations further comprising: responsive to determining that thethermal sensor has failed, generating a notification indicating that thethermal sensor has failed.